The invention relates to the art of controlling sliding mode, for example, to the art of controlling sliding mode used for feedback controlling rotation phase of a camshaft relative to a crankshaft for an internal combustion engine to a target value.
A conventional valve timing apparatus is known as a vane type valve timing controlling apparatus disclosed in Japanese Unexamined Patent Publication 10-141022 such as an apparatus for successively changing opening and closing timing of intake and exhaust valves by changing rotation phase of a camshaft relative to a crankshaft.
This apparatus forms concave portions in the inner surface of a cylindrical housing fixed to a cam sprocket in which vanes of an impeller are accommodated in the concave portions wherein the camshaft rotates relative to the cam sprocket within the range where the vanes of the impeller can move in the concave portions and by relatively supplying and discharging oil into a pair of oil pressure chambers, the vanes are held in the mid position of the concave portions and thus successive changing of rotation phase can be carried out.
When oil pressure of the pair of the oil pressure chambers is adjusted to the level by which a target value of rotation phase can be obtained, a control valve closes an oil pressure passage to stop supplying and discharging oil.
PID (proportional-integral derivative) control is generally adopted as control method of the camshaft rotation phase wherein a control amount is calculated with a deviation (error amount) between an actual angle and a target angle of the camshaft as only one variable.
However, in order to carry out the PID control with a good response characteristic it is preferable that a feedback gain is set variable since viscosity of oil changes with oil temperature and oil pressure, but matching the setting as above is not easy.
In the case of oil pressure control there is wide operation dead band for a switching valve (spool valve) to switch oil supply and oil discharge and therefore dither control is executed with dither components in addition to PID to go beyond the dead band wherein judgement of addition of dither components is required to do with accuracy, bringing a complicated control and more capacity of ROM and RAM. In order to decrease variations of dead band width for each part for securing control accuracy, improvement in machining for parts is required, causing increase of machining costs.
Therefore, there has been considered a sliding mode control which has less influence due to disturbances, instead of a general PID control into.
Then, there is review of application of a sliding mode control into the above oil pressure type valve timing control apparatus and when the sliding mode control is designed according to the conventional theory, the influence due to disturbances such as changes of the oil temperature and the oil pressure is restrained but it is found out that the above sliding control is not effective to the dead band and is no alternative and no supplement for the above dither control.
And also in the case of application of a sliding mode control into a component with a dead band, the feedback control is executed by setting a basic control amount to a central value of an operation dead band and adding a feedback control amount to go beyond the operation dead band to the basic control amount whereby due to component variations and aging deviation between the central value of the operation dead band and the basic control amount may arise, and variations in size of operation dead bands may bring in decrease of response characteristic and occurrence of hunting.
In view of the foregoing, the present invention has an object of carrying out a sliding mode control with higher robust by restraining decrease of response characteristic caused by operation dead band in a control object having the operation dead band to a control amount such as an oil pressure control system.
Another object of the present invention is to provide an apparatus to carry out higher accuracy control in an apparatus with a feedback control by a sliding mode control.
A further object of the present invention is to carry out a control with higher accuracy and in quicker response by avoiding influence caused by component variations and aging by a learning control in a sliding mode control of a control object having operation dead band as above.
The present invention for achieving the above first object is constituted to set a linear term of a control amount as a function of deviation between a target position and an actual position of a control object in an apparatus for sliding-mode controlling a control object having an operation dead band.
Thus even when the actual position of the control object does not change by entering within the operation dead band, since there exists a deviation (xe2x89xa00) between the target position and the actual position of the control object, transfer velocity to the switching line to switch a feedback gain is given properly by a linear term set as the function of deviation, resulting in convergence to the target position with a good response characteristic.
The control object of the present invention may be applied to an oil pressure control system and in the oil pressure control system having a wider operation dead band by a switching valve and the like, the control can be carried out with quicker response by restraining influence caused by the wider operation dead band.
In particular, in a case that a valve timing control apparatus in an internal combustion engine is the control object, wherein rotation phase of a camshaft relative to a crankshaft is controlled variably and successively by the oil pressure control, and the supply and discharge of oil to an oil pressure actuator controlled by oil pressure is selectively controlled by the switching valve, in the oil pressure control type valve timing control apparatus having a wider operation dead band by the switching valve, the control with quick response is carried out by restraining influence due to the dead band.
A linear term may be set by adding a term proportional to the deviation between the target position and the actual position of the control object to a term proportional to operation velocity of the control object.
By this, transfer velocity to the switching line is given properly even on entering into the dead band by a term proportional to the deviation between the target position and the actual position of the control object and when out of the operation dead band, since transfer velocity adjustment function to the switching line caused by a term proportional to operation velocity of the control object is added, more adequate transfer velocity can be obtained and the response can be improved.
A linear term may be set based only on the term proportional to the deviation between the target position and the actual position of the control object.
As described above, even in the case the linear term of the control object is set only by the term proportional to the deviation between the target position and the actual position of the control object, since not only within entering into operation dead band but also out of the operation dead band, transfer velocity to the switching line is given properly, the sliding mode control can be realized and by omitting the term proportional to operation velocity of the control object, easy control (calculation) can be done to thereby save program capacity.
Next, the present invention for achieving the above second object is constituted to feedback control a control object to a target value by correcting a control amount calculated based on a sliding mode control by a dither control.
According to this constitution, based on the sliding mode control, a control with higher robust can be carried out with less influence due to disturbance compared with the feedback control by an ordinary PID control, as well as the control with more accuracy can be carried out based on the correction by the dither control.
Further, a switching function in the sliding mode control may be calculated as a function of a deviation between a target position and an actual position of the control object.
According to this constitution, in the sliding mode control a control amount (non-linear term) corresponding to the deviation can be given and then the feedback control with a good response characteristic can be carried out by the automatic calculation of the control amount to go beyond the dead band and the like.
Moreover, with the correction by the dither control, since the non-linear term is finely adjusted, a highly accurate control can be carried out while securing the optimum response characteristic. In other words, since the dither control requires only an adjustment function to supplement the sliding mode control, the control including additional judgement conditions and the like can be simplified compared with the dither control added to a conventional PID control to thereby save ROM and RAM capacities.
The conditions to which a correction amount by the dither control is added may be set based on the switching function.
Thus since the switching function is calculated as the function of the deviation, the correction amount by the dither control can be added according to the deviation when necessary only. Further, a calculation load for judgement is reduced by carrying over the switching function calculated for the sliding mode control.
The above switching function S may be calculated in the following formula.
S=xcex3xc3x97PERR+d(PERR)/dtxe2x80x83xe2x80x83(1)
xcex3: inclination
PERR: deviation between a target value and an actual value of a control object
d(PERR)/dt: differential value of the deviation
Thus since a switching function S includes the deviation between the target value and the actual value of the control object (PERR) and also a differential value (d) of the deviation, it makes the sliding mode along the switching line more smooth.
The switching function S may be calculated in the following formula.
S=xcex3xc3x97PERR+d(NOW)/dtxe2x80x83xe2x80x83(2)
xcex3: inclination
PERR: deviation between a target value and an actual value of a control object
d(NOW)/dt: actual velocity of a control object
Thus, even when an actual velocity is used instead of the differential value of the deviation d(PERR)/dt, it makes the sliding mode control along the switching line smooth as above.
A control amount U may be calculated in the following formula for the switching function S.
xe2x80x83U=cxc3x97PERR+dxc3x97{d(NOW)/dt}xe2x88x92K{S/(|S|+xcex4)}xe2x80x83xe2x80x83(3)
d(NOW)/dt: actual velocity of a control object
c, d: constant
xcex4: chattering prevention coefficient
In the above formula, a linear term control amount UL expressed by cxc3x97PERR+dxc3x97{d(NOW)/dt} means adjusting velocity of a control system state approaching the switching line (S=0), and a non-linear term control amount UNL means generating the sliding mode along the switching line.
The conditions on which a correction amount by the dither control is added may be set in the following formula.
Sxc2x7xcex94Sxe2x89xa70 or |S|xe2x89xa7S0
xcex94S: variation amount of S
S0: positive predetermined value
According to the above, when a target position of the control object varies from a stationary state wherein a switching valve and the like are in within the dead band, during a time period until the switching valve and the like are out of the dead band, the actual position of the control object does not vary, and so the deviation and the switching function S (both are absolute values and the same hereinafter) continue to increase. That is, Sxc2x7xcex94Sxe2x89xa70. During this period of time, the dither components are added without any condition so that the control object starts to move quickly out of the dead band.
When the control object starts to move out of the dead band, the deviation and the switching function S both start to decrease, however, until the control object approaches the target position to some degree, that is, when |S|xe2x89xa7S0 is satisfied, the addition of the dither components makes the control object approaching the target position quickly, resulting in good response characteristic.
When the control object approaches a target position to reach |S| less than S0, the addition of the dither components is stopped, which restrains overshooting due to excessive control amount to enable quick convergence to the target position.
The above setting of additional condition of the dither components as well as the linear term of the sliding mode control (for example, set proportional to the deviation) have a role of making the control state approaching the switching line (S=0) quickly while restraining overshooting to start the sliding mode along the switching line.
In the case the control object is a valve timing apparatus for an internal combustion engine as above, a control with good response is carried out by restraining influence of the dead band the same as above and also the dither control is used so that the dead band can be carefully adjusted and the control accuracy can be improved.
One aspect of the present invention for achieving the above third object is constituted such that, in a sliding mode control apparatus wherein the feedback control amount to go beyond an operation dead band calculated by a sliding mode control is added to a basic control amount set corresponding to a central value of the operation dead band to the control amount of a control object whereby the feedback control is started and the feedback control is stopped when a deviation between a target value and an actual value of the control object gets within a predetermined dead band, the basic control amount is corrected based on a steady deviation between the target value and the actual value.
In this case, as described above, when the basic control amount deviates from the central value of the operation dead band, the steady deviation between the target value and the actual value of the control object occurs. Therefore, the basic control amount is corrected based on the steady deviation to correspond to the central value of the operation dead band so that a deterioration is response characteristic, occurrence of overshooting and undershooting, and occurrence of steady deviation can be restrained.
Another aspect of the present invention for achieving the third object is constituted such that, in a sliding mode control apparatus wherein the feedback control amount to overcome an operation dead band calculated by a sliding mode control is added to a basic control amount set corresponding to a central value of the operation dead band to the control amount of a control object whereby the feedback control is started and the feedback control is stopped when a deviation between a target value and an actual value of the control object get within a predetermined control dead band, when the deviation gets into the control dead band, while carrying out the feedback control using only a non-linear term and at the same time varying a gain of the non-linear term of the feedback control amount to get the deviation between the target value and the actual value within a set range, the gain is adjusted.
With this constitution, the non-linear term is adjusted to a degree to slightly overcome the operation dead band and therefore chattering does not occur and a good response characteristic is secured.
The switching function S of the sliding mode control may be calculated as a function of the deviation between the target value and the actual value of the control object.
With this constitution, the gain of the non-linear term is switched corresponding to the deviation state, resulting in smooth convergence to the target value.
Further, the switching function S may be calculated by the formula (1) or formula (2) and the effect as described above can be obtained.
Also the control amount U in the above sliding mode control may be calculated by the formula (3), thereby the above described effect can be obtained.
Further, in the case the control object is a valve timing control apparatus for an internal combustion engine as described above, a control with a good response characteristic while restraining influence due to the operation dead band can be carried out and also the above described effect by the invention can be obtained.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.